Robust implementation of high-level envelope sensing (ES) in a VLSI chip is a major challenge. ES is an essential part of many RF systems. One such application is an implementation of the eXcess eNvelope eNhancement (XNN®) technique for power amplifiers (PA), which is disclosed in U.S. Pat. No. 6,437,641 and proposes a solution for efficient enhancement and power boost of wireless power amplifiers, including WiFi and WiMAX power amplifiers.
A typical implementation of an XNN® PA is illustrated in FIG. 1 (Prior Art). The Envelope Sensor (ES) provides high-level detection of the transmitted signals. A conventional technique for detection of RF signals employs diode-based detector. However, such detector diodes are usually capable of handling low power signals in the order of 1-10 mW. The VEC™ circuit (as described in U.S. Pat. No. 6,831,519) requires input signals of the order of 30-300 mW. Therefore, whenever a diode-based detector is used to detect the envelope of the RF signal, it requires amplification, which results in a substantial delay which is unacceptable for most of the XNN® applications.
An RF transistor, operating essentially at a non-linear operating point at the RF frequency range, such as in class B, class AB or class C, might also be used as a detection element. The RF transistor is terminated by a dummy load, or embedded as part of the feedback mechanism in conjunction with the VEC™. The current drawn by the RF transistor is proportional to its RF signal, while the threshold level depends on the biasing condition of its operation class. A detected signal might be obtained by sampling this current and filtering it from RF frequency components. High detection levels, up to few hundred watts, may be obtained this way (for example in WO 03/103149), as shown in FIG. 2 (prior art).
All the methods described above have not yet provided satisfactory solutions to the problem of efficiently sensing the envelope of high level RF signals.
It is therefore an object of the present invention to provide a method and circuitry for efficiently sensing the envelope of high level RF signals.
Other objects and advantages of the invention will become apparent as the description proceeds.